Twisting-torque sensors are devices for measuring torque, the operating principle of which is to measure the torsion on a first shaft, referred to as the transmission shaft, subjected to the torque to be measured, and to compare an angular deformation due to this torsion between the transmission shaft and a second shaft, referred to as the reference shaft, which is not subjected to the torque to be measured. The comparison makes it possible to deduce the torque to be measured.
In particular, the measurement of the angular deformation is done by means of the addition to each shaft of reading teeth forming a phonic wheel, and the acquisition by a sensor of the passage of each tooth in front of the sensor. In the absence of torque on the transmission shaft, a reading tooth on the transmission shaft and a reading tooth on the reference shaft are spaced apart by a certain distance. When the transmission shaft is subjected to a torque, the resulting torsion causes the deformation of the shaft and the movement of a reading tooth on the transmission shaft with respect to a reading tooth on the reference shaft. This movement causes a variation in the time taken for the tooth to pass in front of the sensor compared with a tooth on the reference shaft, and makes it possible to deduce therefrom the torque to which the shaft is subjected.
When such a torque sensor is used in an environment in which high temperature variations prevail, for example in a turbine engine of an aircraft, the torsion on the transmission shaft may be different, for the same torque to be measured, depending on the temperature of the transmission shaft. Thus the angular deformation measured varies in the same way, and the measured torque has an error that is more or less great, depending on the temperature for which the torque sensor was calibrated.
In order to prevent measurement errors due to the variable temperature to which the torque sensor is subjected, several solutions have been proposed.
In particular, one solution proposed is to use inclined reading teeth on the phonic wheel, making it possible to reduce the influence of the temperature. However, the correction made by the inclination of the reading teeth is constant and does not depend on the torque. This correction is therefore optimised solely for one torque range and introduces an error outside this range.
Another solution is to place the torque sensor in a confined environment so that it is not subject to any variations in temperature. However, confining the torque sensor reduces the variations in temperature but does not completely eliminate them. The measurement error is thus not corrected and the measurement precision is affected.
Increasingly accurate torque measurement requirements have led inventors to seek novel solutions in response to these problems.